Constrained mobile bearing hip assembly and method

ABSTRACT

An acetabular hip implant and method includes an acetabular shell component having a first feature and a first insert having a second feature that cooperates with the first feature of the acetabular shell component and further includes a third feature. The implant further includes a second insert having a fourth feature that cooperates with the third feature of the first insert and further includes a fifth feature. A femoral head component includes a sixth feature that cooperates with the fifth feature. Interaction between the first and second features, between the third and fourth features, and between the fifth and sixth features mechanically constrains the acetabular hip implant to prevent dislocation of the femoral head during rotation.

This application is a continuation of U.S. patent application Ser. No.15/005,583 filed on Oct. 13, 2014, now U.S. Pat. No. 9,700,416, which isa continuation of U.S. patent application Ser. No. 14/513,171, now U.S.Pat. No. 9,241,799, which is a divisional application of U.S. patentapplication Ser. No. 13/529,021, now U.S. Pat. No. 8,858,645, theentireties of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to prosthetic orthopaedicimplants, and more particular, to orthopaedic hip implants.

BACKGROUND

Many orthopaedic procedures involve the implantation of prostheticdevices to replace badly damaged or diseased joint tissue. Commonorthopaedic procedures that involve prosthetic devices include total orpartial hip, knee, and shoulder replacements. Hip replacement involvestotal or partial replacement of the hip ball and socket joint.

A total hip replacement procedure typically involves the implantation oftwo main component systems: a femoral component and an acetabularcomponent. The femoral component includes a rigid stem that is anchoredwithin the patient's femur and also includes a head that replaces thepatient's natural femoral head. The acetabular component is implantedwithin the acetabulum of the patient and serves as a bearing surface forthe head of the femoral component. The acetabular component generallyincludes an outer shell configured to engage the acetabulum of thepatient and an inner bearing or liner coupled to the shell andconfigured to engage the femoral head. The femoral head and inner linerof the acetabular component form a ball and socket joint thatapproximates the natural hip joint.

SUMMARY

According to an illustrative embodiment, an acetabular hip implantincludes an acetabular shell component configured to be implanted withinan acetabulum of a patient, the acetabular shell component having afirst feature defined in its inner surface, and a first insert securedto the acetabular shell component such that an outer surface of thefirst surface contacts the inner surface of the acetabular shell.

The first insert includes a second feature defined in its outer surfacewhich contacts the first feature defined in the inner surface of theacetabular shell such that the first insert is permitted to rotaterelative to the acetabular shell component about a first axis andprevented from rotating relative to the acetabular shell component abouta second axis and a third axis.

The first insert having a third feature defined in its inner surface. Asecond insert is secured to the first insert such that the outer surfaceof the second insert contacts the inner surface of the first insert, thesecond insert having a fourth feature defined in its outer surface thatcontacts the third feature defined in the inner surface of the firstinsert. In this manner, the second insert is permitted to rotaterelative to the first insert about the second axis and prevented fromrotating relative to the first insert about the first axis and the thirdaxis

The second insert includes a fifth feature defined in its inner surface.A femoral head configured to be secured to a femoral stem is secured tothe second insert such that the outer surface of the femoral headcontacts the inner surface of the second insert. The femoral headincludes a sixth feature defined in its outer surface which contacts thefifth feature defined in the inner surface of the second insert suchthat the femoral head is permitted to rotate relative to the secondinsert about the third axis and prevented from rotating relative to thesecond insert about the first axis and the second axis.

Interaction between the first and second features, between the third andfourth features, and between the fifth and sixth features mechanicallyconstrains the acetabular hip implant to prevent dislocation of thefemoral head during rotation.

The first feature is different than the second feature, the thirdfeature is different than the fourth feature, and the fifth feature isdifferent than the sixth feature.

One of the first and second features comprises at least one annular orsemi-annular groove and the other of the first and second featurescomprises at least one annular or semi-annular projection that ismovably secured within the at least one annular or semi-annular grooveto permit rotation of the first insert with respect to the acetabularshell about only the first axis.

The at least one semi-annular groove includes two semi-annular groovescentered around the first axis and disposed on opposite sides of theacetabular shell or the first insert. The at least one semi-annularprojection includes two semi-annular projections centered around thefirst axis and disposed on opposite sides of the other of the acetabularshell and the first insert.

One of the third and fourth features comprises at least one annular orsemi-annular groove and the other of the third and fourth featurescomprises at least one annular or semi-annular projection that ismovably secured within the at least one annular or semi-annular grooveto permit rotation of the second insert with respect to the first insertabout only the second axis.

The at least one semi-annular groove includes two semi-annular groovescentered around the second axis and disposed on opposite sides of thefirst or second insert. The at least one semi-annular projectionincludes two semi-annular projections centered around the second axisand disposed on opposite sides of the other of the first and secondinserts.

One of the fifth and sixth features comprises an annular groove and theother of the fifth and sixth features comprises an annular projectionthat is movably secured within the annular groove to permit rotation ofthe femoral head with respect to the second insert about only the thirdaxis.

The annular projection and the annular groove are centered around andsymmetrical about the third axis.

The annular projection and the annular groove are offset from diametersof the second insert and the femoral head.

The first axis is orthogonal to the second axis and the third axis andthe second axis is orthogonal to the third axis.

One of the first and second features comprises a semi-circular grooveand the other of the first and second features comprises a semi-circularprojection that is movably secured within the semi-circular groove topermit rotation of the first insert with respect to the acetabular shellabout only the first axis.

The first feature includes two semi-circular projections disposed onopposite sides of the acetabular shell and the second feature includestwo semi-circular grooves disposed on opposite sides of the firstinsert. The projections and grooves are centered about the first axis toallow for rotation about the first axis.

One of the third and fourth features comprises a semi-circular grooveand the other of the third and fourth features comprises a semi-circularprojection that is movably secured within the semi-circular groove topermit rotation of the second insert with respect to the first insertabout only the second axis.

The third feature includes two semi-circular projections disposed onopposite sides of the first insert and the fourth feature includes twosemi-circular grooves disposed on opposite sides of the second insert.

The projections and grooves are centered about the second axis to allowfor rotation about the second axis.

According to a further illustrative embodiment, an acetabular hipimplant comprises an acetabular shell component configured to beimplanted within an acetabulum of a patient, the acetabular shellcomponent having a first set of projections or grooves defined within aninner surface of the acetabular shell. A first insert is secured to theacetabular shell component such that the outer surface of the firstsurface contacts the inner surface of the acetabular shell.

The first insert includes a second set of projections or grooves definedwithin an outer surface of the first insert and cooperating with thefirst set of projections or grooves defined within the inner surface ofthe acetabular shell. In this manner, the first insert is permitted torotate relative to the acetabular shell component about a first axis.

The first insert includes a third set of projections or grooves definedwithin an inner surface of the first insert. A second insert is securedto the first insert such that the outer surface of the second insertcontacts the inner surface of the first insert. The second insertincludes a fourth set of projections or grooves defined in its outersurface which cooperate with the third set of projections or groovesdefined in the inner surface of the first insert such that the secondinsert is permitted to rotate relative to the first insert about thesecond axis.

The second insert includes a first annular projection or groove definedin its inner surface. A femoral head is configured to be secured to afemoral stem and the femoral head is secured to the second insert suchthat the outer surface of the femoral head contacts the inner surface ofthe second insert. The femoral head includes a second annular projectionor groove defined in its outer surface which cooperates with the firstannular projection or groove defined in the inner surface of the secondinsert. The femoral head is permitted to rotate relative to the secondinsert about the third axis; The first annular projection or groove andsecond annular projection or groove mechanically constrain the femoralhead within the second insert to prevent dislocation of the femoral headduring rotation.

The first set of projections or grooves includes two semi-annularprojections centered around the first axis and disposed on oppositesides of the acetabular shell. The second set of projections or groovesincludes two semi-annular grooves centered around the first axis anddisposed on opposite sides of the first insert. The semi-annularprojections of the first set and semi-annular grooves of the second setare configured to cooperate to allow rotation of the first insert aboutthe first axis.

The third set of projections or grooves includes two semi-annularprojections centered around the second axis and disposed on oppositesides of the first insert. The fourth set of projections or groovesincludes two semi-annular grooves centered around the second axis anddisposed on opposite sides of the second insert. The semi-annularprojections of the third set and semi-annular grooves of the fourth setare configured to cooperate to allow rotation of the second insert aboutthe second axis.

The first and second annular projections or grooves are centered aroundand symmetrical about the third axis and are offset from diameters ofthe second insert and the femoral head.

The first set of projections or grooves includes two semi-circularprojections centered around the first axis and disposed on oppositesides of the acetabular shell. The second set of projections or groovesincludes two semi-circular grooves centered around the first axis anddisposed on opposite sides of the first insert. The semi-circularprojections of the first set and semi-circular grooves of the second setare configured to cooperate to allow rotation of the first insert aboutthe first axis.

The third set of projections or grooves includes two semi-circularprojections centered around the second axis and disposed on oppositesides of the first insert. The fourth set of projections or groovesincludes two semi-circular grooves centered around the second axis anddisposed on opposite sides of the second insert. The semi-circularprojections of the third set and semi-circular grooves of the fourth setare configured to cooperate to allow rotation of the second insert aboutthe second axis.

The first and second annular projections or grooves are centered aroundand symmetrical about the third axis and are offset from diameters ofthe second insert and the femoral head.

Other aspects and advantages of the present disclosure will becomeapparent upon consideration of the following drawings and detaileddescription, wherein similar structures have similar reference numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1 is a perspective view of a first embodiment of an acetabular hipimplant depicted within an acetabulum of a pelvic bone and furtherincluding a stem component extending from a femoral component;

FIG. 2 is an exploded perspective view of the acetabular hip implant ofFIG. 1;

FIG. 3 is a perspective view of the acetabular hip implant of FIG. 1;

FIG. 4 is a plan view of an inner insert of the acetabular hip implantof FIG. 1;

FIG. 5 is an exploded perspective view of a second embodiment of anacetabular hip implant; and

FIG. 6 is a perspective view of the acetabular hip implant of FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Terms representing anatomical references, such as anterior, posterior,medial, lateral, superior, inferior, etcetera, may be used throughoutthis disclosure in reference to both the orthopaedic implants describedherein and a patient's natural anatomy. Such terms have well-understoodmeanings in both the study of anatomy and the field of orthopaedics. Useof such anatomical reference terms in the specification and claims isintended to be consistent with their well-understood meanings unlessnoted otherwise.

Referring now to FIGS. 1 and 2, a first embodiment of an acetabular hipimplant 20 is depicted within an acetabulum 22 of a human pelvic bone24. The acetabular hip implant 20 generally includes an acetabular shellcomponent 26, an inner insert 28, an outer insert 30, and a femoral headcomponent 32. The acetabular shell component 26 is generally configuredto be implanted within the acetabulum 22 of a patient, as seen inFIG. 1. The inner insert 28 is configured to be received within andsecured to the acetabular shell component 26, the outer insert 30 isconfigured to be received within and secured to the inner insert 28, andthe femoral head component 32 is configured to be received within andsecured to the outer insert 30, as will be described in greater detailhereinafter. The femoral head component 32 is configured to be securedto a femoral stem 36, which is configured to be implanted in femoralbone tissue (not shown) of the patient.

As seen in FIGS. 1 and 2, the acetabular shell component 26 includes anouter surface 50 having a generally rounded shape that is hemisphericalor at least partially spherical. The outer surface 50 is configured tobe implanted within the acetabulum 22 using any method or structureknown in the art. The acetabular shell component 26 further includes aninner surface 52 that is partially spherical in shape. In thisembodiment, a plurality of semi-annular projections 70-75 is formedwithin the inner surface 52 of the acetabular shell component 26. Eachof the semi-annular projections 70-75 has a center along an abductionaxis 76 that allow the semi-annular projections 70-75 to cooperate witha feature within the inner insert 28 to allow rotation of the innerinsert 28 with respect to the acetabular shell component 26 about theabduction axis 76, as will be discussed in greater detail below.

While six semi-annular projections 70-75 are depicted in FIG. 2, one ormore projections 70-75 may be utilized. In one embodiment, two centralprojections 72, 73 or a single central projection (not shown) may beutilized. In another embodiment, only projections 70, 75 disposed atopposing axial ends 78, 80 of the acetabular shell component 26 may beutilized.

The inner insert 28, as best seen in FIG. 2, includes an outer surface90 having a generally hemispherical or at least partially sphericalshape and having a size that is slightly smaller than a size of theinner surface 52 of the acetabular shell component 26. The outer surface90 of the inner insert 28 is configured to be received and securedwithin a cavity 92 formed by the inner surface 52 of the acetabularshell component 26. A plurality of semi-annular grooves 94-99 are formedwithin the outer surface 90 of the inner insert 28.

Due to the sizes and shapes of the acetabular shell component 26 and theinner insert 28, the semi-annular projections 70, 75, and thesemi-annular grooves 94-99, the inner insert 28 will only fit within theacetabular shell component with the semi-annular projections 70-75 ofthe acetabular shell component 26 within the semi-annular grooves 94-99of the inner insert 28. The semi-annular grooves 94-99 cooperate withrespective semi-annular projections 70-75 in the inner surface 52 of theacetabular shell component 26 to allow the inner insert 28 to rotaterelative to the acetabular shell component 26 about the abduction axis76. In particular, the semi-annular projections 70-75 form a bearingsurface along which the semi-annular grooves 94-99 ride during rotationof the inner insert 28.

While six grooves 94-99 are depicted in FIG. 2, any number of grooves94-99 may be utilized so long as a number of the grooves 94-99 is thesame as or greater than a number of the projections 70-75 within theacetabular shell component 26. Similarly, the locations of theprojections 70-75 and grooves 94-99 must also correspond to allowinsertion of each of the projections 70-75 into a corresponding groove94-99.

While the acetabular shell component 26 is shown having projections70-75 and the inner insert 28 is shown having grooves 94-99, suchelements may be reversed to allow rotation of the inner insert 28relative to the acetabular shell component 26 about the abduction axis76.

In addition to allowing rotation about the abduction axis 76, theprojections 70-75 and grooves 94-99 cooperate to prevent rotation of theinner insert 28 with respect to the acetabular shell component 26 aboutany other axes, including a flexion axis 100 and an axial axis 102. Theabduction axis 76, in the embodiments shown herein, is orthogonal to theflexion axis 100 and the axial axis 102, and the flexion axis 100 isorthogonal to the axial axis 102. Optionally, the abduction axis 76, theflexion axis 100, and the axial axis 102 need not be orthogonal to oneanother.

Referring again to FIG. 4, the inner insert 28 further includes an innersurface 110 that is generally partially spherical in shape. A pluralityof semi-annular projections 112-117 is defined in the inner surface 110of the inner insert 28. Each of the semi-annular projections 112-117 hasa center along the flexion axis 100 to allow the semi-annularprojections 112-117 to cooperate with one or more feature(s) within theouter insert 30. The semi-annular projections 112-117 and the feature(s)within the outer insert 30 allow rotation of the outer insert 30 aboutthe flexion axis 100, as will be discussed in greater detail below.

The outer insert 30 includes an outer surface 120 having a generallyhemispherical or at least partially spherical shape and having a sizethat is slightly smaller than a size of a cavity 122 formed by the innersurface 110 of the inner insert 28. The outer surface 120 of the outerinsert 30 is configured to be received and secured within the cavity122. A plurality of semi-annular grooves 124-129 is defined in the outersurface 120 of the outer insert 30.

Due to the sizes and shapes of the inner and outer inserts 28, 30, thesemi-annular projections 112-117, and the semi-annular grooves 124-129,the outer insert 30 will only fit within the inner insert 28 with thesemi-annular projections 112-117 of the inner insert 28 within thesemi-annular grooves 124-129 of the outer insert 30. The semi-annularprojections 112-117 and respective semi-annular grooves 124-129cooperate to allow rotation of the outer insert 30 with respect to theinner insert 28 about the flexion axis 100. In particular, thesemi-annular projections 112-117 form a bearing surface along which thesemi-annular grooves 124-129 ride during rotation of the outer insert30.

The outer insert 30 further includes an inner surface 140 that isgenerally partially spherical in shape. The outer insert 30 includes anannular projection 142 spaced inwardly from an outer edge 144 of theouter insert 30 and which is symmetrical about the axial axis 102. Thefunction of the annular projection 142 will be discussed in greaterdetail below.

Still referring to FIG. 2, the femoral head component 32 includes anouter surface 160 having a generally spherical shape and having a sizethat is slightly smaller than the size of a cavity 162 formed by theinner surface 140 of the outer insert 30. The femoral head component 32is configured to be received by and secured within the cavity formed bythe inner surface 140 of the outer insert 30. The outer surface 160 ofthe femoral head component 32 further includes an annular groove 164opposite the femoral stem 36, symmetrical about the axial axis 102, andoffset from a diameter of the femoral head component 32. The femoralhead component 32 is configured to fit within the outer insert 30, suchthat the annular projection 142 of the outer insert 30 snaps into theannular groove 164 of the femoral head 32.

When the acetabular hip implant 20 is assembled, the femoral headcomponent 32 rotates with respect to the outer insert 30 about the axialaxis 102 with the annular projection 142 providing a bearing surfacealong which the annular groove 164 rides. This configuration preventsrotation of the femoral head 32 with respect to the outer insert 30about the abduction axis 76 and the flexion 100 axis.

While the femoral head component 32 is shown with an annular groove 164and the outer insert 30 is shown with an annular projection 142, in analternative embodiment, the femoral head component 32 may include anannular projection and the outer insert 30 may include an annulargroove.

Referring to FIGS. 1-3, when the acetabular hip implant 20 is assembled,the inner insert 28 is secured for rotation about the abduction axis 76within the acetabular shell component 26, the outer insert 30 is securedfor rotation about the flexion axis 100 within the inner insert 28, andthe femoral head component 32 is secured for rotation about the axialaxis 102 within the outer insert 30. This arrangement mechanicallyconstrains the acetabular hip implant 20, thus preventing dislocation ofthe femoral head component 32 during movement.

When the annular projection 142 of the outer insert 30 is disposedwithin the annular groove 164 of the femoral head component 32, thefemoral head component 32 cannot be removed from the outer insert 30without a great amount of force and/or use of a tool. The femoral headcomponent 32 is therefore mechanically constrained to preventdislocation of the femoral head component 32 from the outer insert 28.

As noted above, the semi-annular projections 112-117 and thesemi-annular grooves 124-129 of the inner and outer inserts 28, 30,respectively, allow rotation about the flexion axis 100 with an angle ofrotation of about 90 degrees. The semi-annular projections 112-117 andthe semi-annular grooves 124-129 therefore have a dual function ofrestricting rotation of the outer insert 30 within the inner insert 28and preventing complete dislocation of the outer insert 30 from theinner insert 28. Specifically, with respect to dislocation,semi-circular lips 180, 181 forming a portion of the semi-annulargrooves 124, 129 interfere with the semi-annular projections 112, 117 toprevent movement of the outer insert 30 out of the inner insert 28. Whenforce is exerted on the outer insert 30 (for example, by way of thefemoral head component 32 and/or femoral stem 36), the lips 181, 182interfere with the semi-annular projections 112, 117, respectively, toprevent dislocation.

Similarly, the semi-annular projections 70-75 and the semi-annulargrooves 94-99 of the acetabular shell component 26 and the inner insert28, respectively, allow rotation about the abduction axis 76 with anangle of rotation of about 90 degrees. The semi-annular projections70-75 and the semi-annular grooves 94-99 therefore have a dual functionof restricting rotation of the inner insert 28 within the acetabularshell component 26 and preventing complete dislocation of the innerinsert 28 from the acetabular shell component 26. In particular, withrespect to dislocation, semi-circular lips 182, 183 forming a portion ofthe semi-annular grooves 94, 99 interfere with the semi-annularprojections 70, 75, respectively, to prevent movement of the innerinsert 28 out of the acetabular shell component 26. When force isexerted on the inner insert 28 (for example, by way of the outer insert30, the femoral head component 32, and/or the femoral stem 36), the lips182, 183 interfere with the semi-annular projections 70, 75,respectively, to prevent dislocation.

The mechanisms for restricting rotation of the inner insert 28, theouter insert 30, and the femoral head component 32 combine to constrainthe femoral head component 32 and prevent dislocation of the femoralhead component 32 alone or in combination with the outer insert 30and/or the inner insert 28.

It will be appreciated that the principles of the present disclosure andat least some of the benefits may be carried out in a number ofdifferent ways. For example, FIGS. 5 and 6 depict an alternativeembodiment of an acetabular hip implant 200. The acetabular hip implant200 is similar to the acetabular hip implant of FIGS. 1-4 and, thus,only the differences will be described. As best seen in FIG. 5, a set ofsemi-circular projections 202, 203 is defined in opposing sides 204, 205of the inner surface 52 of the acetabular shell component 26. Thesemi-circular projections 202, 203 in this embodiment, are generallyperpendicular to the abduction axis 76. The semi-circular projections202, 203 are also parallel to each other. The function of thesemi-circular projections 202, 203 will be described in greater detailbelow.

A set of semi-circular grooves 210, 211 is defined in opposing sides212, 213 of the outer surface 90 of the inner insert 28. Thesemi-circular grooves 210, 211 are generally perpendicular to theabduction axis 76 and are parallel to one another.

The inner insert 28 only fits within the cavity 92 formed by theacetabular shell component 26 with the set of semi-circular projections202, 203 disposed within the set of semi-circular grooves 210, 211 suchthat inner surfaces 214, 215 of the semi-circular projections 202, 203are in contact with outer surfaces 216, 217 the semi-circular grooves210, 211. The contact between the inner surfaces 214, 215 and outersurfaces 217 provides a bearing surface for rotation of the inner insert28 with respect to the acetabular shell component 26 about the abductionaxis 76. This arrangement also prevents rotation of the inner insert 28relative to the acetabular shell component 26 about any other axis,including about the flexion axis 100 and/or the axial axis 102.

Still referring to FIG. 5, a set of semi-circular projections 230, 231is defined in opposing sides 232, 233 of the inner surface 110 of theinner insert 28. The semi-circular projections 230, 231 in thisembodiment, are generally perpendicular to the flexion axis 100 andparallel to one another. The function of the semi-circular projections230, 231 will be discussed in greater detail below.

A set of semi-circular grooves 234, 235 is defined in opposing sides236, 237 of the outer surface 120 of the outer insert 30. Thesemi-circular grooves 234, 235 are generally perpendicular to theflexion axis 100 and parallel to one another.

The outer insert 30 only fits within the cavity 122 formed by the innerinsert 28 with the set of semi-circular projections 230, 231 disposedwithin the set of semi-circular grooves 234, 235 such that innersurfaces 238, 239 of the semi-circular projections 230, 231 are incontact with outer surfaces 240, 241 of the semi-circular grooves 234,235. The contact between the inner surfaces 238, 239 and the outersurfaces 240, 241 provides a bearing surface for rotation of the outerinsert 30 with respect to the inner insert 28 about the flexion axis100. This arrangement also prevents rotation of the outer insert 30relative to the inner insert 28 about any other axis including theabduction axis 76 and/or the axial axis 102.

The outer insert 30 of the embodiment of FIGS. 5 and 6 includes anannular projection 142 and the femoral head component 32 includes anannular groove 164, as described in detail with respect to FIG. 2. Thefunctionality of the annular projection 142 and annular groove 164 isalso the same as described with respect to the first embodiment.

Similar to the first embodiment, when the acetabular hip implant 20 isassembled, the inner insert 28 is secured for rotation about theabduction axis 76 within the acetabular shell component 26, the outerinsert 30 is secured for rotation about the flexion axis 100 within theinner insert 28, and the femoral head component 32 is secured forrotation about the axial axis 102 within the outer insert 30. Thisarrangement mechanically constrains the acetabular hip implant 20, thuspreventing dislocation of the femoral head component 32 during movement.

When the annular projection 142 of the outer insert 30 is disposedwithin the annular groove 164 of the femoral head component 32, thefemoral head component 32 cannot be removed from the outer insert 30without a great amount of force and/or use of a tool. The femoral headcomponent 32 is therefore mechanically constrained to preventdislocation of the femoral head component 32 from the outer insert 30.

As noted above, the semi-circular projections 230, 231 and thesemi-circular grooves 234, 235 of the inner and outer inserts 28, 30,respectively, allow rotation about the flexion axis 100 with an angle ofrotation of about _ degrees. The semi-circular projections 230, 231 andthe semi-circular grooves 234, 235 therefore have a dual function ofrestricting rotation of the outer insert 30 within the inner insert 28and preventing complete dislocation of the outer insert 30 from theinner insert 28. Specifically, with respect to dislocation,semi-circular projections 230, 231 interfere with edges forming thesemi-circular grooves 234, 235 to prevent dislocation of the outerinsert 30 from the inner insert 28.

Similarly, the semi-circular projections 202, 203 and the semi-circulargrooves 210, 211 of the acetabular shell component 26 and the innerinsert 28, respectively, allow rotation about the abduction axis 76 withan angle of rotation of about _ degrees. The semi-circular projections202, 203 and the semi-circular grooves 210, 211 therefore have a dualfunction of restricting rotation of the inner insert 28 within theacetabular shell component 26 and preventing complete dislocation of theinner insert 28 from the acetabular shell component 26. In particular,with respect to dislocation, the semi-circular projections 202, 203interfere with edges forming the semi-circular grooves 210, 211 toprevent dislocation of the inner insert 28 from the acetabular shellcomponent 26.

The mechanisms for restricting rotation of the inner insert 28, theouter insert 30, and the femoral head component 32 therefore combine toconstrain the femoral head component 32 and prevent dislocation of thefemoral head component 32 alone or in combination with the outer insert30 and/or the inner insert 28.

The acetabular shell component 26 of any of the acetabular hip implantsdisclosed herein may be formed of any combination of metal, ultra-highmolecular weight polyethylene (UHMWPE), ceramic, polyetheretherketone(PEEK), or any other materials known in the art. In one exemplaryembodiment, the acetabular shell component 26 includes a metal shellhaving an inner surface lined with a polymeric material (or a separatepolymeric component attached to the metal shell). The polymeric materialmay be an ultra-high molecular weight polyethylene (UHMWPE) and themetal may be a higher hardness alloy, such as an alloy of cobalt andchromium, for example CoCrMo. The polymeric insert may be locked,molded, or otherwise secured to the metal shell. In another example, theacetabular shell component 26 has a metal shell with an external surfacethat is provided with a coating that promotes ingrowth of bone tissue.For example, the external surface of the metal shell may have a porousstructure, for example, a coating of cobalt-chromium alloy beads, suchas a product sold by DePuy Orthopaedics Inc. under the trade markPOROCOAT®. Optionally, the external surface of the metal shell may beprovided with a coating of an additional or alternative material thatpromotes bone ingrowth, such as a hydroxyapatite material.

Although the axes 76, 100, 102 are described as aligning with theanatomical axes (i.e., abduction, flexion, axial), the axes 76, 100, 102may alternatively be aligned in another manner, so long as the axes 76,100, 102 are orthogonal to one another. Optionally, the abduction axis76, the flexion axis 100, and the axial axis 102 need not be orthogonalto one another.

The acetabular hip implants disclosed herein allow the three basicmotions of the hip to be broken down into three different movements. Thecombined rotational capabilities of these three different movements,namely, movement of the inner insert 28 with respect to the shell 26about the abduction axis 76, movement of the outer insert 30 withrespect to the inner insert 28 about the flexion axis 100, and movementof the femoral head component 32 with respect to the outer insert 30about the axial axis 102, provides a large range of motion of thefemoral head component 32 relative to the acetabular shell component 26.The embodiments disclosed and described in detail herein provide thislarge range of motion in a manner that prevents dislocation of any ofthe components of the acetabular hip implant.

While two inserts 28, 30 are depicted in the figures herein, it shouldbe understood that a single insert 28 or 30 may be utilized.

In an exemplary implementation, the acetabular implant 20 is used in atotal hip replacement procedure. A surgical method for implanting theacetabular hip implant 20 of FIGS. 1 and 2 involves assembling thecomponents 26, 28, 30, and 32 of the acetabular hip implant 20 andimplanting the acetabular hip implant 20 within the acetabulum 22 of thepatient while supporting the femoral stem 36 within the femoral bonetissue.

In further detail, a reamer, not shown, is typically used to ream orotherwise cut the acetabulum 22 in order to form a hemisphericallyshaped cavity. The surgeon may then implant either final components ortrial fit components. Trial fitting is well known in the art and assiststhe surgeon in final preparation of the acetabulum and in choosing theproper sizes of the various components of the acetabular hip implant 20.

After suitable trial fitting, the trial implant is removed and thesurgeon may then implant the acetabular shell component 26 into theacetabulum 22. The acetabular shell component 26 may be press fit,bolted, cemented or otherwise attached to the acetabulum 22, as is wellknown in the art.

In a first exemplary procedure, the acetabular shell component 26 isimplanted into the acetabulum 22 separately and then the inner insert 28is pressed into the acetabular shell component 26 in vivo. The innerinsert 28 is aligned with the acetabular shell component 26 such thatthe semi-annular projections 70-75 or semi-circular projections 202, 203of the acetabular shell component 26 are received within thesemi-annular grooves 94-99 or semi-circular grooves 210, 211 of theinner insert 28 to allow rotation of the inner insert 28 with respect tothe acetabular shell component 26 about the abduction axis 76. Theacetabular shell component 26 is therefore stationary and the innerinsert 28 rotates about the abduction axis 76.

The outer insert 30 is pressed into the inner insert 28 in vivo.Optionally, the outer insert 30 may be pressed into the inner insert 28external to the acetabulum 22. As noted above, the outer insert 30 isaligned with the inner insert 28 such that the semi-annular projections112-117 or semi-circular projections 230, 231 of the inner insert 28 arereceived within the semi-annular grooves 124-129 or semi-circulargrooves 234, 235 of the outer insert 30 to allow rotation of the outerinsert 30 with respect to the inner insert 28 about the flexion axis100. The inner insert 28 is therefore stationary with respect to theflexion axis 100.

Once the inner and outer inserts 28, 30 are secured, the surgeon securesthe femoral head component 32 within the outer insert 30. The femoralstem 36 may already be implanted within the femoral bone tissue or maybe implanted within the femoral bone tissue after the femoral headcomponent 32 is secured within the outer insert 30. To secure thefemoral head component 32 within the outer insert 30, the femoral headcomponent 32 is pressed into the outer insert 30 until the annularprojection 142 of the outer insert 30 snaps into the annular groove 164of the femoral head component 32. The positioning and shape of theprojection 142 and the groove 164 allow the femoral head component 32 torotate with respect to the outer insert 30 about the axial axis 102. Theouter insert 30 is therefore stationary with respect to the axial axis102.

In the embodiment described above, the components of the acetabular hipimplant 20 are assembled in vivo. Alternatively, any of the components(or all) may instead be assembled external to the acetabulum 22 prior toimplantation. In addition or alternatively, one skilled in the artshould understand that the same steps may be utilized (minus insertionof the outer insert 30 into the inner insert 28) if the outer insert 30is omitted.

As will become apparent from reading the present specification, any ofthe features of any of the embodiments disclosed herein may beincorporated within any of the other embodiments without departing fromthe scope of the present disclosure.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the apparatus, system, and method describedherein. It will be noted that alternative embodiments of the apparatus,system, and method of the present disclosure may not include all of thefeatures described yet still benefit from at least some of theadvantages of such features. Those of ordinary skill in the art mayreadily devise their own implementations of the apparatus, system, andmethod that incorporate one or more of the features of the presentinvention and fall within the spirit and scope of the presentdisclosure.

The invention claimed is:
 1. An acetabular hip implant, comprising: an acetabular shell component configured to be implanted within an acetabulum of a patient, the acetabular shell having a first feature defined in its inner surface, a first insert secured to the acetabular shell component such that an outer surface of the first insert contacts the inner surface of the acetabular shell, the first insert having a second feature defined in its outer surface which contacts the first feature defined in the inner surface of the acetabular shell such that the first insert is (i) permitted to rotate relative to the acetabular shell component about a first axis and (ii) prevented from rotating relative to the acetabular shell component about a second axis and a third axis, the first insert having a third feature defined in its inner surface, a second insert secured to the first insert such that the outer surface of the second insert contacts the inner surface of the first insert, the second insert having a fourth feature defined in its outer surface that contacts the third feature defined in the inner surface of the first insert such that the second insert is (i) permitted to rotate relative to the first insert about the second axis and (ii) prevented from rotating relative to the first insert about the first axis and the third axis, the second insert having a fifth feature defined in its inner surface, and a femoral head extending along the third axis, from a first end configured to be secured to a femoral stem, to a second end, the femoral head being secured to the second insert such that the outer surface of the femoral head contacts the inner surface of the second insert, the femoral head having a sixth feature positioned at the second end, opposite the femoral stem when the femoral head is secured to the femoral stem, the sixth feature being defined in its outer surface which contacts the fifth feature defined in the inner surface of the second insert such that the femoral head is (i) permitted to rotate relative to the second insert about the third axis and (ii) prevented from rotating relative to the second insert about the first axis and the second axis; wherein the sixth feature is annular, symmetrical about the third axis, and offset from a diameter of the femoral head, and wherein interaction between the first and second features, between the third and fourth features, and between the fifth and sixth features mechanically constrains the acetabular hip implant to prevent dislocation of the femoral head during rotation.
 2. The acetabular hip implant of claim 1, wherein one of the fifth and sixth features comprises an annular groove and the other of the fifth and sixth features comprises an annular projection that is movably secured within the annular groove to permit rotation of the femoral head with respect to the second insert about only the third axis.
 3. The acetabular hip implant of claim 2, wherein the first axis is orthogonal to the second axis and the third axis, and the second axis is orthogonal to the third axis. 